The present invention relates to polymer nano-strings, methods for their preparation, and their use as, for example, additives for rubber, including natural and synthetic elastomers. The invention advantageously provides several mechanisms for surface modifications, functionalization, and general characteristic tailoring to improve performance in rubbers, elastomers, and thermoplastics.
Tires are often subjected to rough road conditions that produce repetitive, localized high-pressure pounding on the tire. These stresses can cause fatigue fracture and lead to crack formation and growth. This degradation of the tire has also been referred to as chipping or chunking of the tread surface or base material.
In an attempt to prevent this degradation, it is known to add reinforcements such as carbon black, silicas, silica/silanes, or short fibers. Silica has been found advantageous due to its ability to deflect and suppress cut prolongation, while silanes have been added to bind the silica to unsaturated elastomers. The fibers that have been added include nylon and aramid fibers.
It is also known that the addition of polyolefins to rubber compositions can provide several beneficial properties. For example, low molecular weight high density polyethylene, and high molecular weight, low density polyethylene, are known to improve the tear strength of polybutadiene or natural rubber vulcanizates. In the tire art, it has also been found that polyethylene increases the green, tear strength of carcass compounds and permits easy extrusion in calendaring without scorch. Polypropylene likewise increases the green strength of butyl rubber. Polypropylene has also been effective in raising the static and dynamic modulus of rubber, as well as its tear strength.
Although the addition of polyolefins to rubber compositions is known to provide several beneficial effects, the addition of polyolefin to tire recipes may also have a deleterious effect on other mechanical and wear properties of tires, as well as handling and ride of the tire.
Polymer nano-particles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonics. Similarly, vinyl aromatic (e.g. polystyrene) microparticles have been prepared for uses as a reference standard in the calibration of various instruments, in medical research and in medical diagnostic tests. Such polystyrene microparticles have been prepared by anionic dispersion polymerization and emulsion polymerization.
Nano-particles preferably are monodisperse in size and uniform in shape. However, controlling the size of nano-particles during polymerization and/or the surface characteristics of such nano-particles can be difficult. Accordingly, achieving better control over the surface composition of such polymer nano-particles also is desirable.
Nano-particles can serve as discrete particles uniformly dispersed throughout a host composition. Rubbers may be advantageously modified by the addition of various polymer compositions. The physical properties of rubber moldability and tenacity are often improved through such modifications. Of course, however, the simple indiscriminate addition of nano-particles to rubber is likely to cause degradation of the matrix material, i.e., the rubber characteristics. Moreover, it is expected that the selection of nano-particles having suitable size, material composition, and surface chemistry, etc., will improve the matrix characteristics. Polymer nano-strings may also serve as a reinforcement material for rubber compositions in order to overcome the above-mentioned drawbacks of polyolefin and silica reinforcement. Polymer nano-strings are capable of dispersing evenly throughout a rubber composition, while maintaining a degree of entanglement between the individual nano-strings, leading to improved reinforcement.
In this regard, development of polymer nano-strings having a surface layer which would be compatible with a wide variety of matrix materials is desirable because discrete strings could likely disperse evenly throughout the host to provide a uniform matrix composition. However, the development of a process capable of reliably producing acceptable nano-strings has been a challenging endeavor. Moreover, the development of a solution polymerization process producing reliable polymer nano-strings advantageously employed in rubber compositions, has been elusive.